Thunderstorm over Profitis Ilias, Santorini, Greece. A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterised by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds and often heavy rain. Strong or severe thunderstorms include some of the most dangerous weather phenomena. This storm was observed on October 1rst, 2018 at sunrise.